How can we improve PostJoint?

My offer was declined but seller wrote to me to negotiate a better rate. I agreed, but I can not go in the system and re accept this offer

I made an offer to a seller, he declined but asked if he could negotiate a better rate for less work on my part. I agreed to post at another price. The system will not let me go in and re accept this offer. It just keeps saying OFFER DECLINED. So how can I go in and re accept an offer at a different price than I originally bid